1. Field of the Invention
The present invention relates to a method of manufacturing an integrated cantilever drive mechanism, a method of manufacturing an integrated prove drive mechanism, a cantilever drive mechanism manufactured by the aforesaid method, a probe drive mechanism manufactured by the aforesaid method, a scanning tunnel microscope (STM) which utilizes the aforesaid mechanism and an electronic device such as an information processing apparatus which utilizes the principle so as to record and/or reproduce information at high density.
2. Related Background Art
Recently, an STM capable of directly observing the electronic structure of surface atoms of a conductor has been developed (G. Binnig et.al., Phys. Rev. Lett. 49 (1982) 57) so that an actual space image can be measured at a significantly high resolution (nanometer or less) regardless of the fact that the material is single crystal or amorphous structure.
The STM utilizes a phenomenon that a tunnel current passes when voltage is applied to a portion between a metal probe and a conductive material and they are brought closer at a distance of about 1 nm and the aforesaid current is changed expotentially because it is very sensitive to the change in the distance between the two elements.
By scanning the probe while maintaining the tunnel current at a constant level, the surface structure in an actual space can be observed at a resolution of an order of an atom. Although the analysis to be performed by using the STM is adapted to only the conductive materials, it has been applied to the analysis of the structure of a thin insulating film formed on the surface of the conductive material.
Furthermore, the aforesaid apparatus or means employs a method of detecting a small electric current so that an advantage is realized in that the observation can be performed with a small amount of electricity while preventing damage to the medium. In addition, wide use of the STM has been expected because it can be operated in the atmosphere.
In particular, the practical application of the STM to serve as a high density recording/reproducing apparatus has been positively promoted as disclosed in Japanese Patent Laid-Open No. 63-161552 and Japanese Patent Laid-Open No. 63-161553. The aforesaid high density recording and/or reproducing apparatus is so arranged that a probe similar to that of the STM is used to perform recording while changing the voltage to be applied to a portion between the probe and a recording medium. As the recording medium, a thin layer made of a .pi.-electron type organic compound is used, which is a material having a switching characteristic with a memory capability of voltage-current characteristics. The reproduction is performed by utilizing the change in the tunnel resistance between the region which has been subject to the aforesaid recording process and a region which has not been subjected to the same.
As the recording medium adapted to the aforesaid recording method, a medium the surface shape of which is changed due to the voltage applied to the probe is able to perform the recording/reproducing operations. In a case where the STM is operated or the recording/reproducing operation by using the STM is performed, the distance from the probe to the sample or the recording medium must be controlled to an order of .ANG.. Furthermore, the two-dimensional scanning of the probe must be controlled to an order of several tens of .ANG. in the recording/reproducing operation for the purpose of recording/reproducing information items arranged two-dimensionally on the medium. In addition, in order to improve the function of the recording/reproducing system, and in particular, to raise the processing speed, an arrangement has been disclosed in which a multiplicity of probes are selectively driven to detect the tunnel current.
That is, the relative position between the probe and the medium must be three-dimensionally controlled at the aforesaid accuracy in a region in which a multiplicity of the probes are disposed. The aforesaid control is performed by using a laminated-type piezoelectric device or a cylindrical piezoelectric device, or the like fastened to a portion including the probe or a portion including the medium.
However, since the aforesaid devices are not suitable to be integrated although a large quantity of change can be allowed, it is disadvantageous to employ them in a multi-probe type recording and/or reproducing apparatus.
In the aforesaid viewpoint, a method has been disclosed in which the probe is fastened on a cantilever having a length of hundreds of .mu.m and the cantilever is driven by a piezoelectric member (C. F. Quate et al., Transducer, '89, lecture No. D3.6, June 1989. IEEE Electron Device Letters 10 (1989), Nov. No. 11).
A method of manufacturing a conventional cantilever will now be described with reference to the drawings.
FIG. 12 illustrates the overall body of a cantilever probe. A substrate 1 is made of silicone, and an actuator (drive portion) is formed into a cantilever having a piezoelectric bimorph structure. The actuator has a zinc oxide layer, a dielectric layer and a metal electrode stacked alternately. FIG. 13 is a cross-sectional view which illustrates the cantilever shown in FIG. 12. The cantilever is arranged in such a manner that an upper electrode and a lower electrode are disposed while being vertically separated from each other and a thin electrode for the tunnel tip is disposed at the central portion of the free end portion. By suitably combining the way the voltage reaches the portion between the electrodes, the electrode can be moved in three axial directions.
The aforesaid cantilever is formed as follows:
First, the silicon substrate is subjected to an anisotropic etching process so as to reduce the thickness of the region, which will be formed into the cantilever, to about several tens of .mu.m. An electrode 9 is made of metal such as aluminum and a piezoelectric layer 8 made of zinc oxide or the like is formed by a sputtering method. Each piezoelectric layer is held between silicon nitride films by a plasma CVD (Chemical Vapor Deposition) method.
The upper electrode is covered with gold in order to prevent undesirable oxidation of the surface of a tunnel chip 11. After the overall body of the cantilever has been formed, polyimide is applied to the surface to a thickness of several .mu.m. A silicon membrane is removed by plasma etching effected from the reverse side of the wafer and the polyimide is removed by oxygen plasma, so that the cantilever is formed.
However, since driving of a plurality of the cantilevers, detection and/or amplification of the tunnel current and feedback of the drive from the tunnel current must be selectively performed at the time of the recording/reproducing operation, switching circuits, bias circuits, amplifying circuits and servo circuits and the like must be provided for the purpose of realizing the aforesaid functions. The aforesaid circuits must be formed on the same substrate on which the cantilever is formed in order to reduce the size and to raise the processing speed.